


Playing With Yourself

by equilateral_asshat



Category: Gravity Falls
Genre: Archived From My Tumblr, F/M, Interdimensional Frickle Frackle, Multi, Rule 63 AU, Swappleganger AU, pinecest - Freeform, pinescest - Freeform
Language: English
Status: Completed
Published: 2018-12-15
Updated: 2018-12-15
Packaged: 2019-09-18 11:51:19
Rating: Explicit
Warnings: No Archive Warnings Apply
Chapters: 1
Words: 4,513
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/16994478
Author URL: https://archiveofourown.org/users/equilateral_asshat/pseuds/equilateral_asshat
Summary: This one is set in the rule 63 multiverse AU thing Pinewreaths on tumblr wrote a year or two back.





	Playing With Yourself

“So according to what you’ve told me, the twins mysteriously just popped into your dimension, after stumbling into my lab in our dimension, because I left it unlocked?”

Dipper could feel himself sweating bullets; roughly half an hour beforehand, Cassie and Mason’s Great Aunt Juliet had managed to get a lock on their home dimension and contacted Grunkle Ford. Together, the two had quickly managed to put their heads together and opened a stable portal between the two planes of reality. Now Ford was staring incredulously at him and Mabel as he went over the details of the fib they had told to explain their showing up here, in Universe K45[&]rs.

Juliet merely nodded confirmation at Ford, who glanced over and narrowed his eyes at his niece and nephew. Mabel managed to wear a face of apologetic innocence, but Dipper? He was never good at that. He fidgeted in his seat, glancing past his Grunkle, through the doorway to the kitchen and met Cassie’s eyes. She shot him a hopeful grin and shrugged.

“Well…” Ford continued, before sighing and pinching the bridge of his nose. “It is highly likely that I might have _accidentally_ left things less secure than I typically do. I’ve been studying anomalies around the Ring of Fire in the Pacific and it’s consuming a lot of my time and thoughts.”

“Anomalies?” Juliet inquired hopefully. “Maybe I can help, and we could exchange notes? I’m honestly dying to see what kind of things you’ve seen in your travels through the Multiverse. Surprised we never managed to cross paths when I was stuck dimension hopping too!”

“So I’m not the only version of me that got stuck jumping from one reality to the next? Interesting! Perhaps we could go down to the lab and take some time to exchange notes,” Ford confirmed, grinning wide at her. He then cleared his throat. “Dipper, Mabel, you two stay out of trouble while myself and Juliet go down to her lab to discuss our theories and compare findings. I’ll come find you when it’s time to head home. We’ll discuss you nosing around in my lab-locked or otherwise-later, back in our own dimension.”

They had only been out of the room for a moment before Mabel started to stand up. Dipper immediately yanked her back down.

“You see?! You see how much trouble you’ve gotten us in?!” he chastised. “And all because you thought it would be fun to, how did you word it again? ‘Frickle Frackle on the sciency console stuff’,” he finished, crossing his arms with a huff. “Now when we finally get back home Ford’s gonna read us the riot act.”

“Sooo… are you saying you didn’t like the labcoat and the goggles and stuff?” she quipped. Dipper drug his hands down his face in frustration.

“That’s the only reason you got me to agree in the first place,” he grumbled. “So when we get back home and into the lab, we’ll uh… we’ll grab those.” She giggled at him, standing up again and prancing out of the room.

“Hey, Mason! Looks like we’re stuck here for awhile while our Grunkle nerds out with your Graunt, wanna show me more of your hoodie collection?”

“Sure thing!”

And like that, Mabel and her gender-swapped double were scampering off to another part of the Shack. Dipper flopped next to Cassie with a sigh, shaking his head.

“Where do those two get all of that energy?” Cassie wondered aloud, watching the pair run off hand in hand. Dipper shrugged.

“I blame the sugar, personally,” he noted, rubbing at his forehead while his free hand fell to the couch cushions. Before he could start drumming his fingers with frustration, he felt the oddly familiar grip of Cassie’s hand closing overtop it.

His pace quickened, and if he was certain of one thing it was that his palm was probably as sweaty as Cassie’s felt. Moreso, even. Another thing he was certain of, was that his shorts suddenly seemed a bit too small. His thighs pressed together for a bit as he tried to mentally quell that instinctive response to a girl’s touch. Even if that girl was an attractive female version of himself.

“So, uh, just wondering if maybe you wanted to spend whatever time you have left in our dimension, doing… I dunno, anything? We can go look at the list of conspiracies I’ve been tracking, or discuss mystery story tropes or like, makeout and other stuff?” she suggested, blushing. He felt red creeping up his own face.

With nothing more than a nod and a hop to his feet, the pair were off towards the attic. The second they were behind the door, Cassie’s lips were on his.

His brain buzzed with static; their hands never stopped moving, never stopped touching. He lost track of whose fingers were whose. Who lifted up his shirt? Was he the one that undid Cassie’s shorts?

… well technically, it was him. And her. Both of them, right? They shared most of the same DNA from what he could theorize. So it didn’t matter who did what in this scenario, so much, because technically whatever happened, it was the same person doing it, for the most part.

“W-wait,” he muttered between kisses, her lips smothering his again. With a gentle push, he found himself sitting back on the bed, lap straddled. “Wait a moment, I have a question!”

“I’m actually pretty open minded, despite my uptight facade, so just understand that unless I say no you can keep going,” Cassie said with a matter-of-fact tone. With a playful chuckle he settled back further, hands on her shoulders.

“No no, nothing like that,” he stated. She raised an eyebrow in confusion, blowing a curly strand of hair out of her eyes. “I just realized that we’re pretty much the same person-”

“Uh huh…” she sighed, pressing her lips to his neck in _that_ particular spot. He was about to wonder how she would know about it, but realization brought him right back to his original question.

“W-would that make what we’re about to do incest or masturbating?” he managed to sputter, to which Cassie groaned and sat up, peeling her shirt off as she went..

“No, nope. That’s not what we’re here to discuss. We’re here to discuss your genitals and my genitals getting reintroduced.” Instinctively, she grabbed at one of his hands and placed it against one of her newly freed breasts. He must have missed when her bra came off. He wasn’t particularly observant when he had a girl’s face on his own.

“But I mean, we share _most_ of the same DNA,” he went on, and she sucked the thumb of his other hand into her mouth, tongue twirling around the end. He shuddered, toes curling. “B-but not all of it, clearly,” he remarked, giving the soft mound of flesh in his hand a playful, emphasizing squeeze.

Popping off of his thumb, Cassie nibbled at the very end of it. “So what?”

“So, is us doing this counted as playing with ourselves in some weird interdimensional way, or is it technically just more incest?” Her hips ground down against his as she growled in frustration, and he was suddenly very aware of shorts growing tighter still.

“That’s not important right now!” she demanded.

“Aren’t you curious, though?!” he blurted.

“Of _course_ I am!” she half shouted back. “But we both know that if you don’t shut your mouth, right this second, you’re never going to end up inside me because we’re going to be sitting here in this room, half undressed, debating the odd theoretical quandary of this situation!” She glared at him, and he felt himself shrink back down onto the bed. She clearly noticed his reaction, because she frowned apologetically and rubbed at her neck. “Sorry, I just-”

“No, no, you’re right.” He tugged her down to join him, lips locking once more. They both chuckled into the embrace, each set of lips moving against the other tenderly. At some point each of them hooked fingers into his waistband and tugged it down, followed shortly by his boxers.

The heat he felt when her flesh touched his own caused them both to shiver. Her hips rocked, a trail of moisture gliding along the underside of his shaft. A pair of muttered ‘oh fuck’s escaped either of them. Her thighs clamped down tightly against his hips, and his hands found her waist in a matter of moments. As she adjusted her position, their eyes met, and they paused for a brief second.

“But we’re gonna talk about it after, right?”

“Oh, definitely!”

With one swift motion, hips met hips, and he was inside her.

=========

A few rooms away, it looked like a storm had passed through and scattered sweaters and hoodies to the walls. They were piled up in random spots, with a hint of organization apparent by the fact that certain colors were piled together. In the center of this mess, on a pile of red fabric, two naked bodies ground together.

Mabel’s head was buried in the material under herself, muffling her squeals of pleasure. From behind, Mason had a firm grip on her hips, his lap meeting her backside time and again. Each of them were covered with a fine sheen of sweat, and had apparently leapt immediately into their romp the second they were behind closed doors.

Mabel’s body trembled as she felt herself drawing closer to that proverbial edge, breaths more labored as the coil in her stomach tightened, as though every thrust Mason gave was winding a mechanism inside of her. Suddenly, the tension snapped, and Mabel buried her face once more, pleasured cries dying in the rat’s nest of red tops beneath their joining.

Mason kissed between her shoulderblades, and up along her neck to just under her ear, each of them giggling all the while. Mabel’s eyes fluttered open as his grasp on her sides adjusted, and then she let out a playful shriek as he spun her over, letting them face one another. One pair of braces flashed at the other as each grinned. Then, a thought crossed her mind, and it was clearly visible on her face, because Mason canted his head to the side.

“Sup?” he offered.

“Well, it just occurred to me that we’re like, genderswapped doppelgangers of each other,” she noted, “so we’re not exact copies but we’re pretty much related.”

“Uh huh?” he helpfully chimed in, hands playing over her sides and hips. She squirmed with a languid grace.

“So does that make this more incest or weird, interdimensional-self-diddlin’?”

Mason’s face took on a thoughtful look, lips pursed, eyebrows scrunched. After a few seconds he shrugged.

“Does that really matter at this point, though?”

With a smirk and a shake of her head, Mabel’s legs snaked out and wrapped around Mason’s hips.

“Nope, now get back in there, we gotta get one more in before we crash the constellation party in the attic!”

Soon enough, the sounds of flesh on flesh continued.

=========

Foreheads pressed to one another, Dipper and Cassie rocked together. Somehow in the odd, limb-entangling way that lovemaking works, they had changed positions several times, almost on accident each time.

They had started out with her on top, and over the course of the next half hour ended up on their sides, then Dipper on top, then in some sort of yoga-esque pose Cassie suggested, and finally had ended up back with him on top after almost falling out of the bed. There had been a brief squawking of fright and flailing of arms in that moment, which ended with laughter and an agreement to save the Kama Sutra things for more stable, less creaky terrain (apparently across the vast multiverse, no version of the shack had stable beds in the attic).

Hips were pushed and rolled firmly together, each set of legs quivering. One of Dipper’s hands had strayed southwards, thumb circling the bud of flesh that marked the peak of Cassie’s womanhood. Each time his thumb passed over her flesh, it felt like little jolts of electricity passed through her hips and up her spine. They had been like this for awhile, Dipper certain to be more patient, more sensual than their first, hurried tryst had gone.

They had just pressed their lips together with a pair of pleased sighs when the door snapped open loudly.

“HA! Toldja they’d be goin’ slow this time, cough it up buddy!” a pantsless Mabel demanded, holding a hand out to a shirtless Mason. He pressed a red bill into her hand, eyes rolling. Cassie and Dipper both sat up with a scream, each grabbing the sheets to censor themselves, wrestling for a majority of the covers.

“Mabel?! What the hell, can’t you be quiet about this stuff?!” Dipper objected.

“Pfffft, relax man,” Mason interjected. “Graunt Juliet is still down in the lab with your Grunkle, and Julianna is out cold.” He held up a tiny earbud of some sort. “And I got’er hearing aide, so there’s no way she’ll hear anything.”

Cassie groaned and pinched the bridge of her nose in frustration. “You know, just because she taught you how to be a deviant doesn’t mean you have to apply the skills constantly.”

“Well yeah, oh sister mine, but how else am I gonna make sure nobody else discovers the weird escapade of forbidden no-no-touching we four have all decided to engage in? Besides, Graunt Anna will probably just tell me I did good.”

Dipper grunted, and Cassie made an exaggerated “oof!” sound as Mabel flopped across both sets of laps. Mason strolled over, joining her a bit further down, pinning legs beneath bedspread.

“So, what brings you in here to interrupt us,” Dipper asked, glaring a little at his sister. “Again.”

“Same as last time, bro-bro,” Mason replied, and Dipper found it a little irritating that it sounded so natural coming out of he doppelganger twin’s mouth. Mostly because it made his loins stir to hear it said in that husky, yet sweet tone Mason produced when smooth talking. “We figure this might be our last chance to have us a little fun all at once!”

“So whatcha say, sister?” Mabel cut in, reaching up to twirl a finger in Cassie’s curls. “Shall we?”

Cassie shook her head with exasperation, then glanced over at Dipper. He offered a shrug, and a small, amused grin.

“Hey, I’m down if you are,” Dipper noted. “Besides, I think I have an idea for what we can all do this time. As one big group, even!”

“I think I see what you’re putting out there,” Cassie replied, grinning. There was a sudden flurry of movement, sheets being thrown over the intruding siblings. Squeals of laughter rang out as bodies all wrestled for control. When the proverbial dust settled, the twins all found themselves in an interesting position indeed.

In the chaos, Mason’s pants had gone missing, and he had been laid flat on his back. Everybody else had ended up on top of him, in a way. Cassie was firmly positioned over his face, facing his legs. Mabel was straddling his midsection, and Dipper had gotten his shoulders under Mason’s knees, their respective lengths crossed together like swords.

“Well, this looks like a world of fun for m-mmfff!” Mason began, but Cassie smothered his voice by taking a seat. Not even a split second later she shuddered, gasping as she wiggled her hips.

“Oh god, I’m gl-glad you can use that tongue for things other than blabbing all the time,” she teased, leaning forward to plant her lips on Mabel’s. Dipper’s twin whimpered into the kiss as his hands sought out her chest, snaking under the fabric of her sweater and giving each nipple a playful tweak. Once Cassie broke off the kiss, he peeled the sweater away.

“So, where do I fit in all this?” she asked with a tease, glancing over her shoulder at her brother. His reply was simply to grab her hips and yank back, until Mason’s tip prodded at her backside. “Eep!”

“You fit _on_ ,” he emphasized, lifting her slightly, then maneuvering a hand to position Mason’s member against her folds, “this right here.” With a soft tug, he filled his sister with her gender-swapped self. Her body shook, and before she could make another sound, Cassie’s hands were on her face, pulling her in for another feverish kiss. Dipper admired the sight, sucking on his fingers, working up a mouthful of spit.

“In the meantime,” he continued as he spat his fingers out, smearing them under Mason’s sack, lubricating the hidden ring of flesh there, “this is where I fit in.” Cassie sniggered to herself, while both Mabel and Mason let out sarcastic groans at the pun.

Dipper merely shrugged, prodding at the slick entryway softly. Mason’s body tensed, then eventually relaxed, hips rocking invitingly. Leaning forward, he let his weight do most of the work until he felt flesh yield, and within a flash he was halfway to hilted. Apparently Mason was much more accustomed to this sort of thing than he was.

He pulled back an inch or so then pressed forward again, then repeated the motion again, and again until he finally felt his thighs come to rest against Mason’s backside. His hands sought out his sister’s hips, and one managed to dip in along her inner thigh. The touch coaxed shivers from her, which goaded him onwards. As his fingers sought out the place where she and Mason’s flesh met, she moaned into Cassie’s lips.

Cassie echoed the moan, her hips pushing down, forcing her backside and nether regions against her brother’s face. Never once did he protest; instead, his tongue darted out with passionate vigor, the tip swirling over any bit of flesh it could find. As far as his sister seemed to be concerned, anything it could reach was fair game. Every touch seemed to light her nerve endings ablaze with pleasure, and she vocalized every bit of it into the wet, hungry kisses she shared with Mabel.

Mabel’s body trembled. The soft lips on her own, the sounds of pleasure filling the room, her brother’s hands-one on her muffin, teasing both her and Mason, while the other ran upwards, fingertips drawing tiny lines over her belly before falling on her breast, combined with the amazingly full feeling she got while her hips rocked against her double’s was almost too much to deal with at once. She whined into the next kiss, breaking it to twist her head to the side. Reaching back, she got a handful of her brother’s hair and yanked him around to smother his lips with her own. Cassie pouted and ran a thumb along Mabel’s cheek, biting at her lower lip.

As soon as Mabel released the hold on her brother, she swiveled back around, facing Cassie before grabbing her shoulders and tugging her in for a kiss that was just as feverish as her last. Her hips slammed down into Mason’s as Cassie squirmed, the passionate liplock triggering something within her. The attention of both mouths on her, from either end, was clearly something that was able to set her off.

Her squirming hips crammed down, hands dragging nails along her brother’s chest, leaving tiny, harmless pink trails in their wake. She panted into the kiss she shared with Mabel, before breaking it to let out a pleasured wail as her body was wracked with tremors; this time she was apparently first in line on the orgasm train.

Mason, rendered mostly immobile, did his part to squirm as he was both mildly suffocated by his twin’s crotch and rear, and stuffed from the other end by her doppelganger, as well as pinned under his own double at the hips. It was all too much for him as well, and before long he felt that telltale tick as his member flared up with the first pulse of climax, before unleashing rope after rope of hot, white stickiness against Mabel’s inner walls. The waves of his orgasm were further obvious to Dipper, who felt the muscles around his girth squeezing with a familiar rhythm.

Soon the clenching muscles were too much for him, and he drove his hips forward one last time, burying himself in Mason’s backside before his own climax hit. His length throbbed as he painted Mason’s innards with his seed, his teeth softly digging into his sister’s shoulder as he came. His hips gave an involuntary, tiny shove with every pulse of his orgasm, while his fingers worked furiously over his sister’s clit. There was no way he was coming down off of this alone. Luckily, he wouldn’t.

Watching, feeling, and hearing everybody else get off, plus her brother’s practiced fingers, brought Mabel to the brink swiftly. Her thighs clamped, knees digging into Mason’s hips as her body quaked. A high pitched, blissful cry of release warbled out of her throat. Every nerve ending felt like it was on fire, her toes curling, fingers clenched. Her pussy milked Mason for every drop he was worth as she rode out her final climax, shoulders pushing into her brother’s chest as she moaned and sighed, shivering every time a new wave of pleasure shot through her synapses, making her giggle.

Shortly thereafter, all they had all managed to untangle themselves from one another, there were four simultaneous flops onto the bed, as well as shared declarations of “I love you” all around. While they all basked in the afterglow, an ominous creak broke through the silence.

“What th-” Dipper began, but was cut off by the sensation of the world falling out from under them. Or, well, the bed falling out. The legs at the foot of the bed had been rocked loose during their foursome, and the continued application of four teenager’s weight had been the final straw. There was a loud bang of the frame hitting the floor, and four panicked yelps as both sets of twins rolled to the ground.

“Well, that was hopelessly loud,” Cassie griped as she began gathering and tossing clothing to the others, who all swiftly tugged on clothing. Dipper had to put his shirt on three times; first it was inside out, and then backwards. “Let’s go make sure we didn’t manage to wake up Graunt Anna or there’ll be hell to pay.”

A quick look confirmed that Cassie and Mason’s Great Aunt was still sat in her large, garish purple recliner in front of the TV. Her loud snores echoed throughout the room. With a collective sigh of relief, the four tried to think up their next plan of action; an excuse as to how the bed broke. None of them thought telling their elders that it was a big sinful four-way would go over well.

“Just tell’em we were watching cartoons on your laptop, Cass,” Mason insisted. “It doesn’t seem THAT far fetched. These guys have never seen any of our cartoons before.”

“Now I wanna watch them for real,” Mabel complained, scuffing the floor as they approached the vending machine.

“You’ll get a chance, after all your Grunkle and our Graunt seemed to think they had a stable connection from your dimension to ours,” Cassie said. A code was punched into the vending machine’s panel, and soon they were descending the hidden stairs to the lab.

“So uh, who does the talking here?” Dipper asked as they came to the door of the lab. Mason grabbed Cassie’s wrist and held her hand aloft.

“I nominate Cass, she’s a better liar than I ever was,” he insisted. She tugged her arm free, but shrugged and nodded.

“Yeah he’s right.” Gripping the handle on the doorway to the lab, she took a deep breath, preparing the fib in her mind before opening the door. With a twist, she swung the door open. “Uh, Graunt Juliet, we were watching some cartoons upstairs when the bed br-OH MY GOD!”

All four twins wore shocked, if not somewhat terrified expressions. Ford and Juliet quickly stepped apart, each adjusting their glasses. Juliet gave her hair a quick brushing with her fingers. Ford seemed to be completely unaware that he had a smear of lipstick across his face.

“Children, you should know better than to enter a lab unannounced, all of you! We were exchanging some very discreet information,” he half lied, adjusting his shirt’s collar. However, from the back of the group, a titter of giggles rose. Mason couldn’t stop laughing. “And just what is so funny, young man?”

“We caught you playin’ with yourselves!” he said with a teasing, sing-song tone. Ford had red creeping up his face, and Juliet cleared her throat loudly.

“I vote we come to an agreement of sorts to establish that none of your ever saw any of this happening.” Ford raised an eyebrow her direction. “What’s it going to take to keep you all quiet? If Julianna finds out about all of this I’ll never hear the end of it.”

The foursome of twins all regarded one another, then huddled up. After a few quick seconds of discussion, they broke apart, Cassie coughing to focus attention on herself.

“We have, after some deliberation, come to a decision,” she said with a businesslike voice.

“Yeah yeah, cough up the blackmail,” Ford grumped.

“Well, Grunkle Ford, you and Juliet have stabilized the portal from our world to yours, riiiight?” Mabel inquired. He nodded.

“Oh, of course! It’s very stable. You could almost come visit anytime you wanted if you knew the coordinates.” Juliet slapped a hand over her face, shaking her head. “Uh, why do you ask, Mabel?”

“If we’re gonna stay quiet about you two,” Mason began, “we wanna be able to visit each other’s worlds whenever.”

Ford and Juliet shared a glance. Ford shrugged. Juliet sighed and nodded.

“Very well,” she relented. “As long as you stay quiet about this, we’ll make arrangements to set up some sort of visitation privileges.”

A round of high fives and excited, victorious whooping went up amongst the twins. Ford smirked, leaning over to Juliet. “Do they think we don’t know why they want it?”

“Shut up or I’m not ‘swapping notes’ with you anymore,” she teased, winking at him.

“Oh please,” he fired back, rolling his eyes. “We both know that you’re just lying to yourself.”

With a groan, Juliet shook her head. “We’re going to have to establish if it’s incest or masturbatory next visit.”

“I told you, it has to be incest,” Ford mumbled. “Different chromosomes, but mostly shared DNA.”

“And I vote that doesn’t matter, you’re technically me, and I you, so it’s some sort of roundabout two person masturbation!” Juliet whispered back as the four sets of twins ran back up the stairs. Once they were certain they were alone again, she wrapped an arm around Ford’s shoulders, moving in to leave more lipstick stains on his face before a moment of realization hit.

“Wait… did they say the bed broke?!”

-END


End file.
